Cutting 3" thinwall copper drain

I’m remodeling a 1950’s bath where all of the DWV is plumbed with 3″ copper. I need to extend one of the arms of the stack with a Fernco to new PVC. What’s the best way to cut large copper tube without a huge tubing cutter? My first thought was a sawzall with a metal blade, but would an angle grinder or maybe even a dremel work better? I'm really worried about deformation and maybe even tearing this stuff as I cut it.

 

Keep in mind that the thinnest part of an old copper drain pipe is typically going to be the 6 o’clock position where it’s been eroded over the years. I’d cut the bottom of the pipe first with a long “thin kerf” blade on a sawzall. If the pipe cracks lengthwise at the bottom, go back to your next brass fitting and cut the copper pipe off flush with the brass fitting. The brass fitting is typically about the same O.D. as pvc pipe so that you can join the two with a two band no-hub coupling.

 

I wouldnt be scared of the sawsall approach. Angle grinder with cutoff wheel should be ok too or the dremmel . Be a good idea to use ppe . just takes a minute gloves sleeves and eye protection face shield maybe even a mask why breath any of that?
no hub adapter band 3 1/8 od copper to 3 inch pvc ( 3 1/2) whatever the true id is but readily available at plumbing suppliers

 

That's the fast one. Definitely eye protection.